When Chris Hempel learned that her twin daughters had a fatal genetic disease, she took on the pharmaceutical industry and the FDA to try to find a cure. A story of incredible determination and love

Perched at the kitchen island in her home, 10 miles from the pulsing neon strip of Reno, NV, Chris Hempel pulls out a pink Shutterfly photo album and flips through its pages. She smiles, as every mother does when reminiscing about her children as babies, but her eyes also mist over while she revisits the early life of her twin daughters. She runs a finger down the milestones she documented: Addison's first words were "outside" and "open"; Cassidy's were "doggie" and "duckie." They walked early, at 10 months. The photos are adorable  naked babies blowing bubbles and smearing vanilla frosting all over their faces, bright-eyed toddlers hell-bent on climbing over furniture, mischievous little girls unleashing flash floods at the water cooler. "They just got into stuff," Chris says, laughing. "They were super -happy, smiling all the time."

Her gaze moves to her daughters, 7 at the time of this visit, slumped at a toddler table, their eyes unfocused and distant. Chris sits down to feed them, lifting the spoon with encouraging coos that are met with an occasional grunt, but mostly silence. Tiny pieces of turkey and pineapple miss the girls' mouths and land in the hard plastic bibs circling their necks. Cassi flails her hands about, refusing to eat. She can barely keep her head steady.

After lunch, Chris's husband, Hugh  a no-nonsense bear of a man whose serious disposition melts around his daughters  carries Addi and Cassi to a room down the hall, where they sit on miniature overstuffed chairs covered in white sheets and watch cartoons most of the day. Chris returns to the album and pages back to images of the girls on tricycles at age 3. "We noticed they weren't pedaling right," she says. At first, the signs of trouble were vague: The twins didn't seem to be running like other kids, or they'd walk and suddenly their heads would flop backward. Then they came down with a virus. In Chris's view, there was an instant change. "Their eyes were just delirious," she says. It was right around their third birthday, and they couldn't shake their sickness.

As the weeks bled into months, Chris knew something was seriously wrong: "I could see these subtle things  like their balance was off. And their eyes didn't seem to be tracking right. Other people thought I was crazy," she says. "My family kept telling me the girls were fine."

Then, during an exam, the girls' pediatrician found that their spleens were swollen to four times the normal size. Chris took them straight to Lucile Packard Children's Hospital at Stanford Medical Center in Palo Alto, CA. Over the course of five visits, they were seen by top immunologists, geneticists, and hematologists, none of whom could figure out what was wrong with Chris's daughters.

That would take another 18 months.

Although all the tests came back negative, Chris was sure the girls  who were, after all, identical twins  had a genetic condition. Then she noticed troubling new neurological symptoms, especially a faint slippage into slurred speech, and e-mailed the geneticist at Stanford  who realized there was one disease he hadn't tested for.

It was an extremely rare genetic disorder called Niemann-Pick Type C disease (NPC), which affects only about 250 children in the U.S. Chris immediately Googled it and was devastated. NPC, she read, was a defect on the gene that regulates cholesterol metabolism in the cells. Harmful amounts of the fatty lipid (which our bodies make continuously and normally excrete) accumulate in the spleen, liver, lungs, bone marrow, and, ultimately, brain, leading to neurological deterioration that can trigger seizures and loss of motor skills like walking, holding a pencil, even swallowing. NPC is sometimes dubbed "childhood Alzheimer's" because it leads to severe dementia.

Chris had the girls' skin biopsies rushed to Stanford. Two weeks later, on October 17, 2007, the hospital called and confirmed her worst fear: Her daughters had NPC. As they watched, Chris ran out of the house, crying hysterically. How can this be? she thought. They're talking and singing and playing with the neighbor's dog and having fun at school. And now they're going to lose their minds and die?

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